An electrode pad provided on the surface of a package that houses an IC or LSI has two types: one is a ball grid array (BGA) that belongs to a surface-mounting type (BGA package), and the other is a pin grid array (PGA) that belongs to a through-hole-mounting type (PGA package). Of these, in the PGA package, pin electrodes protruding perpendicularly from the surface of a semiconductor package are inserted into an ordinary socket having mechanical terminals. Thus, the semiconductor package is mounted on a printed circuit board provided with the socket.
The types of the socket to be used for the PGA package include a low-inserting-force socket (LIF socket), a zero-inserting-force socket (ZIF socket), and a socket using an anisotropic electroconductive sheet.
The LIF socket is provided with (a) a made-of-resin base housing in which inserting holes are formed and (b) spring contacts that are held in the inserting holes of the base housing, extend through the base housing, and have tail portions that are soldered to a printed circuit board to which the socket is mounted. When the pin electrodes of the PGA package are placed in the inserting holes of the LIF socket, the spring contacts in the inserting holes are expanded or deflected. Thus, the elastic force of the spring contacts connects the pin electrodes with the spring contacts mechanically and electrically. Consequently, the PGA package is electrically connected with the printed circuit board to which the LIF socket is mounted (see the published Japanese patent application Tokukai 2002-343524 (Patent literature 1)).
The ZIF socket is provided with (a) a made-of-resin base housing in which inserting holes are formed in the shape of a grid, (b) a metallic contacts held in the inserting holes of the base housing, (c) a made-of-resin cover housing provided with through holes arranged in the shape of a grid through which pin electrodes can be inserted, (d) a sliding mechanism that slides the cover housing against the base housing, and (e) an operating lever. When the operating lever is turned upward or downward, the cover housing is slid against the base housing. Consequently, the PGA package is electrically connected with the printed circuit board to which the ZIF socket is mounted (see the published Japanese patent application Tokuhyouhei 11-513837 (Patent literature 2)).
As the socket using an anisotropic electroconductive sheet, there is a socket in which socket electrodes made of conductive rubber or the like are formed on an electrically insulating substrate, and the socket electrodes are provided with through holes for inserting the pin electrodes. As the conductive rubber, a material is used in which carbon or metallic particles are dispersed in organic rubber such as silicone rubber (see the published Japanese patent application Tokukaishou 63-259981 (Patent literature 3)). The socket electrodes made of conductive rubber are formed at the inner walls of metallic pipes that penetrate through the insulating substrate or formed at the metallic inner walls in the through holes of the substrate (see the published Japanese patent application Tokukaihei 05-226022 (Patent literature 4) and the published Japanese utility model application Jitsukaihei 03-091669 (Patent literature 5)). The foregoing Patent literatures state that these anisotropic electroconductive sheets can provide stable connection regardless of the shape of the inserted pin electrodes, and the pin electrodes are reliably held on account of the flexibility of the conductive rubber.                Patent literature 1: the published Japanese patent application Tokukai 2002-343524        Patent literature 2: the published Japanese patent application Tokuhyouhei 11-513837        Patent literature 3: the published Japanese patent application Tokukaishou 63-259981        Patent literature 4: the published Japanese patent application Tokukaihei 05-226022        Patent literature 5: the published Japanese utility model application Jitsukaihei 03-091669        